Open trash fires have been commonly used by the US military in conflicts after the September 11 attacks, and are lit to get rid of everything from plastic bottles to human waste and old tires -- all incinerated with jet fuel.

But the fumes from these holes in the ground are suspected of causing a range of illnesses among soldiers, from chronic respiratory ailments to a variety of cancers.

Biden believes the pits are at the root of the brain cancer that claimed the life of his son Beau, who served in Iraq in 2008.

By 86 votes to 11, the Senate passed the PACT Act, which expands the window of eligibility for free medical care and ensures that, for certain respiratory illnesses and cancers, veterans will get disability benefits without having to prove they were made sick by exposure to the pits.

The passage came just days after Republican senators had rejected the bill, triggering withering condemnation from veterans groups and activists, including the outspoken comedian Jon Stewart, who had championed the cause.

Biden welcomed the approval of the act, saying, "While we can never fully repay the enormous debt we owe to those who have worn the uniform, today, the United States Congress took important action to meet this sacred obligation."

He said the new law would be "the biggest expansion of benefits for service-connected health issues in 30 years and the largest single bill ever to comprehensively address exposure to burn pits."